Fiber-reinforced composite materials are used as lightweight, high-strength materials. A fiber-reinforced composite material is constructed by combining reinforced fibers and a matrix of resin, metal or the like. Therefore, the kinetic properties (mechanical properties) of the fiber-reinforced composite material are improved more than those of the matrix. Hence, the fiber-reinforced composite material is suitable for structural components such as fuselages and wings of aircraft. Especially, the use of a resin as the matrix can further decrease the weight of the fiber-reinforced composite material. In particular, in applications in which high performance is required, a laminated reinforcing material formed by laminating a plurality of fiber bundle layers formed of fibers arrayed in one direction is used. In this case, the plurality of fiber bundle layers function as a reinforced fiber base material, and are respectively laminated in different array directions of the respective fiber bundle layers.
The following countermeasures have been carried out or proposed against warpage (bending and torsion) of fiber-reinforced composite materials employing a laminated reinforcing material.
(1) Laminated structures are made symmetrical in order to cancel the moment generated.
(2) A mold is made in expectation of the amount of warpage to bring the form after deformation within the accuracy required.
(3) The laminated reinforcing material is reheated and compressed after molding for correction of warpage.
(4) Fibers having different torsional moments are used to constitute a fabric, thereby cancelling the moment generated (for example, see Patent Document 1).
Without relation to the countermeasures against warpage, a fiber-reinforced laminated structure as disclosed in Patent Document 2 has also been proposed. According to the invention disclosed in this document, the thickness of an isotropic composite material can be decreased as compared with the case where a plurality of fiber sheets are laminated while the fiber orientation angle is changed by 15°, 30°, 45° or 90°. In this case, the fiber orientation angle θ between adjacent fiber sheets among the laminated fiber sheets is 60°<θ<90°. Inversely symmetrical cases as shown in the following table are also indicated as examples of the lamination pattern. The phrase “inversely symmetrical” refers to the case where the positivity and negativity of the lamination pattern are inverse at both sides of a standard surface. In Table 1, the standard surface is a surface on which a fiber sheet having a lamination pattern of 0° is disposed.
TABLE 1Number offiberFibersheetsorientationlaminatedangleLamination pattern572°−36/72/0/−72/36726°−77/−51/−26/0/26/51/77751°26/77/−51/0/51/−77/−26777°−51/26/−77/0/77/−26/51980°−20/60/−40/80/0/−80/40/−60/20
The above prior art involves the following problems.
In the case (1), when the fiber-reinforced composite material has a complicated form, not a flat-plate like form or a form obtained merely by bending a flat plate, there exists a site in which no symmetrical laminated layer can be constructed. FIG. 8(a) shows a fiber-reinforced composite material 51 of a skin-web structure composed of three sets of symmetrical laminated sheets 52. According to this configuration, two symmetrical laminated sheets 52 are respectively bent to constitute a skin part 53 and a web part 54. As shown in FIG. 8(b), when the fiber orientation angles of the fiber bundle layers constituting the respective symmetrical laminated sheets 52 are defined as 0°, 90° and ±45°, the left and right sides of a neutral surface near the web part 54 are not symmetrical. FIG. 8(c) shows the case where the same symbols are used for the layers having a fiber orientation angle of 45° as the uppermost layers in the skin parts 53 of the symmetrical laminated sheets 52 disposed at the left and right sides, respectively. As shown in FIG. 8(c), the symbols for the layers having a fiber orientation angle of 45° of the respective symmetrical laminated sheets 52 are opposite with respect to the facing surfaces of the left-side symmetrical laminated sheet 52 and right-side symmetrical laminated sheet 52 as the border. As a result, torsion occurs in the fiber-reinforced composite material 51.
In the case (2), trial production for obtaining data on the amount of warpage is required, which increases the production cost and number of steps.
In the case (3), correcting steps are additionally required after molding, which increases the production cost.
In the case (4), since commercial unidirectional materials or fabrics cannot deal with the problem, the cost for materials is increased.
Also, a configuration in which fiber sheets are laminated in the state where the fiber orientation angles are merely inversely symmetrical as in Patent Document 2 cannot reduce torsion.